The following minutes reflect the discussions and events that transpired during the second meeting of the Aquifer Committee Working Group meeting. The descriptions contained herein have been distributed to the Working Group in draft form; comments that were received from the Working Group have been incorporated into this version and should be considered final.
The second meeting of the Working Group was held in the O'Conner Room at the Savannah Civic Center.
1) The following persons were in attendance on July 24, 2001:
Bill McLemore was unable to attend due to a schedule conflict. Larry Keegan served as an observer; John Cox serves as Chairman of the Working Group.
2) The meeting convened at 9:00 AM and was called to order at 9:10 AM. The first order of business addressed several typographical errors in the minutes of the first meeting. The typographical errors and corrections are as follows: a) Page 2, paragraph 4), item d), third sentence. Add "to" immediately before "whether." The corrected sentence should read as follows, "Camille raised the question the question as to whether the salinity profile observed was the result of connate water being flushed out of the confining unit or saline shallow water migrating vertically downward."
b) Page 2, paragraph 4), item e), first sentence. Add "the" immediately before "off-shore." The corrected sentence should read as follows, "John Clarke indicated that the off-shore drilling program had drilled core holes at distances of seven, ten, and fifteen miles off-shore of Tybee Island."
c) Page 3, paragraph 7), item c). Change "date" to "data." The corrected sentence should read as follows, "Classical statistical analyses may be inadequate because the data are clustered and biased."
d) Page 3, paragraph 7), item d). Change "objective" to "objectives." The corrected sentence should read as follows, "The objectives of geostatistics are to calculate the most accurate predictions, quantify the accuracy of the predictions, design optimal sampling plans, and to quantify the worth of the data."
3) John Cox spent a few minutes re-iterating the purpose of the Working Group (to develop a plan of study that upon implementation will determine what impact the proposed deepening of Savannah Harbor to -48 feet will have upon the Upper Floridan aquifer) and the Technical Concerns that have been recommended to and accepted by the Aquifer Committee ([a] How much of a rate and quantity of leakage increase resulting from harbor deepening is unknown. [b] Changes in chloride concentrations with time in the Upper Floridan aquifer caused by harbor deepening are unknown. [c] Hydraulic properties, salinity and hydraulic head of the Miocene unit are poorly known, as is the variability of these parameters. [d] Hydraulic properties and geometry of the previously identified paleochannels are poorly understood. [e] The geologic framework is not as well refined as it should be.).
4) Fred Falls (USGS, South Carolina) presented preliminary findings of this summer's offshore drilling program that was conducted as part of the Sound Science Initiative. The following major points were discussed:
a) The geology at the 8-mile site (distance measured from northeast end of Tybee Island) as well as specific conductance of ground-water samples collected from the Upper Floridan aquifer suggest that salt-water is leaking into the aquifer at this location.
Inspection of cores recovered during drilling, indicated that the Miocene section was essentially absent at this site (approximately 1.5 feet of Miocene sediments overlie the Upper Floridan at the 8-mile site. Specific conductance of ground-water samples collected from the Upper Floridan aquifer was approximately 25,800 uS (seawater would be expected to have specific conductance of about 50,000 uS). The tops of various stratigraphic horizons at the 8-mile site were consistent with those at the 7-mile and 10-mile sites. The geology at the 15-mile site is confusing inasmuch as the top of the Oligocene section is significantly deeper than at the other offshore sites. The 8-mile site was chosen based on seismic reflection data that suggested that the confining unit had been breached and that the location was within an offshore paleochannel.
b) The Calibogue Sound core hole was located about one mile northeast of the northeast end of Daufuski Island, behind Hilton Head Island. This location was also picked based on seismic reflection data that suggested that the Miocene section was either breached or significantly thinned. The geology at the Calibogue site consisted of channel sand overlying about 40 feet of apparently low permeability gray clay. The clay apparently serves as an effective aquitard, but is not typical of Hawthorn Group marine clay units.
Specific conductance values of ground-water samples collected from the Upper Floridan aquifer at the Calibogue Sound site were low, indicating that saltwater has not invaded the aquifer at this location.
c) At three of the four offshore drilling locations (7, 8, and 10 mile sites) the freshwater/saltwater interface appears to be deeper than 700 feet msl.
d) Samples were collected from the 8-mile and Calibogue Sound sites for pore water and isotope analyses
5) Camille Ransom (SCDHEC) and Jim Landmeyer (USGS, South Carolina) discussed the results obtained from the Bull River Rotosonic site.
a) The current hydraulic head within the Upper Floridan aquifer at the Bull River site is approximately -40 feet; the pre-development head was approximately +25 feet.
b) The geology at the Bull River site consists of sands, muddy sands, and shell hash within the upper 55 feet of section. At -55 feet, a coarse, well-sorted, quartz sand unit was encountered; this unit extended to a depth of about -75 feet and was interpreted as channel infill (paleochannel).
c) The Miocene section extended from about -75 feet to -120 feet and consisted of silty to sandy clay. The cores recovered from this section appeared to be dry, but when placed in hydraulic press, samples yielded pore-water and samples were collected for chloride and isotope analyses.
d) The top of the Upper Floridan aquifer (Oligocene) was found at about -120 feet and consisted of a limey sand. The Eocene section was encountered at -192 feet and consisted of porous, hard limestone.
e) There were certain mechanical problems using the Rotosonic drill rig within the coarse sands of the paleochannel. Freshwater was placed within the core barrel and drill casing to overcome hydrostatic pressure and prevent flowing sands from locking the core barrel within the casing. The head within the casing was probably sufficient to push freshwater into the coarse sands of the channel infill, hence affecting the chloride concentrations reported from this section. A Geoprobe was subsequently used to collect representative ground-water samples from the channel infill.
f) The analytical results from this site indicated that a chloride concentration gradient is present within the Miocene section. Chloride concentrations of approximately 8,000 mg/l were reported within the surficial section; chloride concentrations declined to about 2,000 mg/l in the -75 to -80 feet interval. Assuming 50 mg/l chloride concentration to represent saltwater affects, approximately 88% of the Miocene section has been affected by saltwater.
g) Vertical hydraulic conductivity values as determined from laboratory permeameter tests were reported as follows:
76.5 - 77.5 foot interval: 1.2E-7 cm/sec
79.0 - 80.0 foot interval: 2.2E-7 cm/sec
82.5 - 83.5 foot interval: 1.5E-7 cm/sec
85.0 - 86.0 foot interval: 2.5 E-7 cm/sec
90.0 - 91.0 foot interval: 8.2E-8 cm/sec
93.5 - 95.0 foot interval: 3.5E-8 cm/sec
100.0 - 101.0 foot interval: 3.8E-8 cm/sec
101.0 - 106.0 foot interval 4.0E-8cm/sec
115.0 - 116.0 foot interval: 4.5E-8cm/sec
6) Harold Gill presented the results of the aquifer test feasibility study that he completed at the request of GAEPD. Harold also discussed the results of an industrial pumping cut-back that occurred in 1996.
a) The results of a 72 hour pumping test conducted at Tybee Island were re-evaluated using the techniques discussed by Trescott, Pinder, and Larson. The analysis involved calculating the dimensionless time required for a uniform hydraulic gradient to be established across a confining unit and to develop leakage from an overlying aquifer or stream bed using:
tD = Kl t/Ssb2 where: tD = dimensionless time
Kl = vertical hydraulic conductivity of confining unit
t = time since pumping began
Ss = specific storage of confining unit, and
b = thickness of confining unit.
Transient effects of downward leakage from storage in the confining unit are dominant when dimensionless time is less than 0.5. After transient effects have dissipated, a uniform gradient across the confining unit is established and a consequent "flow through" component of steady leakage is established.
Using available data and published literature for estimates of values of the input parameters, several scenarios were calculated to determine various potential values of dimensionless time. Several of the scenarios produced values of dimensionless time greater than 0.5, hence suggesting that several of the pumping scenarios may induce leakage from the confining unit and that useful field data may be derived to determine values of vertical hydraulic conductivity of the confining unit. It was suggested that a pumping test of 30 days duration may be appropriate.
b) Harold then discussed an industrial pumping cut-back that occurred during the summer of 1996 and the possibility of researching water-level records for well JAS-112 (Jasper Count, South Carolina), that is thought to open to the Miocene section to determine the recovery that occurred in this well and using those data to calculate vertical hydraulic conductivity within the Miocene.
Rick Krause remarked that JAS-112 may actually be JAS-1 and that it may actually be open to the Upper Floridan aquifer, not the Miocene. Camille Ransom and John Clarke placed telephone calls to their respective staffs to verify the location, identification, and well depth. It was subsequently reported that the subject well is open to the Upper Floridan, not the Miocene.
c) For purposes of this discussion, it was decided to refer to pumping tests as "aquitard tests" since it is the hydraulic properties of the aquitard that are of concern.
d) The Working Group was in consensus that a pilot aquitard test or tests be conducted to determine if useful hydraulic field data may be obtained.
e) There was some discussion as to the most appropriate place to conduct a pilot aquitard test. Ultimately, the Working Group agreed that a pilot test should be conducted at the Fort Pulaski monitoring well cluster.
8) Following Harold Gill's presentation the Working Group broke for lunch.
9) The meeting resumed at approximately 1:15 PM. The remainder of the afternoon was dedicated to discussions of various study plan elements that would address the technical concerns.
10) The meeting adjourned at approximately 5:00 PM
11) The meeting reconvened at 9:00 AM July 25, 2001. The following persons were in attendance:
12) Discussion regarding appropriate study plan elements and their relationship to the technical concerns continued throughout the morning. Ultimately, ten elements were identified that if implemented would address the technical concerns. The study plan elements are as follows:
a) Conduct a reconnaissance level of drilling using Rotosonic coring methods. Coring should be completed at strategic sites that, when completed, would form a transect through a significant portion of the cone of depression. Core holes should be completed at Tybee Island, Ft. Pulaski, across the Savannah River from the northern end of Elba Island, the north end of Hutchinson Island, and at a control site near Ridgeland, South Carolina. The Bull River site should be a part of the transect, but will not be re-drilled. Cores should be examined and the lithology described, samples should be collected for determination/analysis of porosity, vertical hydraulic conductivity, pore water geochemistry, and grain-size distribution. Geophysical logs should be run at each core hole location to include velocity, spontaneous potential, electrical resistivity, and natural gamma.
b) The jack-up rig should be used to drill selected sites immediately adjacent to the navigation channel at selected locations based on the data collected from land-based transect. Similar parameters should be analyzed as in the land-based transect.
c) A pilot scale aquitard test should be conducted by pumping the upper portion of the Upper Floridan aquifer and recording water level responses in the strata overlying the Upper Floridan aquifer.
1. The pilot scale aquitard test should be conducted at Ft. Pulaski.
2. Install an appropriate number of piezometers at the test site, including one in the Upper Floridan aquifer (probably six).
3. Assume that a new pumping well may need to be constructed.
d) Evaluate and analyze aquitard test data and determine usefulness of conducting additional aquitard tests.
e) Complete piezometer clusters at each transect location. The Hutchinson Island site should have top priority.
f) Complete additional seismic profiles. Two parallel lines should be run down each side of the navigation channel from Fields Cut to several miles offshore as well as several tie lines and an attempt to re-survey South Channel.
g) Conduct research to obtain pumping and dredging records to the degree that such may be available.
h) Synthesize the field data into a working data base or graphical representation (pre-modeling phase).
i) Complete two-dimensional numerical model to predict flux in chloride concentration through the strata and into the Upper Floridan aquifer beneath the navigation channel.
j) Complete lateral solute-transport model using the navigation channel as a line source to predict migration and dilution of chloride plume in the Upper Floridan aquifer, if necessary.
13) At times the discussion addressed specific elements in great detail; the Working Group agreed that specific details could be addressed as the plan of study is developed and that at present, these 10 elements serve as a conceptual framework for a plan of study.
14) The meeting was adjourned at approximately 12:00 pm.